Wet material reduction mill



Nov. 28, 1961 D. WESTON WET MATERIAL REDUCTION MILL 5 Sheets-Sheet 1Filed Feb. 9 1959 Nov. 28, 1961 D. WESTON WET MATERIAL REDUCTION MILL 5Sheets-Sheet 2 Filed Feb. 9, 1959 Nov. 28, 1961 D. WESTON 3,010,651

WET MATERIAL REDUCTION MILL Filed Feb. 9, 1959 5 Sheets-Sheet 3 Nov. 28,1961 D. WESTON WET MATERIAL REDUCTION MILL 5 Sheets-Sheet 4 Filed Feb.9, 1959 Nov. 28, 1961 D. WESTON WET MATERIAL REDUCTION MILL 5Sheets-Sheet 5 Filed Feb. 9. 1959 in mm W 2 m 1 MM] m m f/ m n m I Q. MM /N D M MN I NN M m 3 mm piH H QB |I|| N\ m QMN @N N saw QR QNN vNUnited States Patent 3,010,661 WET MATERIAL REDUCTION MILL David Weston,Toronto, Ontario, Canada, assignor to Aerofall Mills Inc., Columbus,Ohio Filed Feb. 9, 1959, Ser. No. 792,025 Claims priority, applicationCanada Jan. 28, 1959 13 Claims. (Cl. 241-30) The reduction of materialsin the wet state has for many years been a conventional practice in agreat many metallurgical and industrial milling operations. One of thegenerally accepted limitations of wet has been the necessity to maintainseparate milling stages for the reduction of different particle sizeranges of materials. Thus a conventional plant for the wet reduction ofmaterial has generally consisted of a number of stages of crushingdesigned to reduce the material to a suitable rod or ball mill feed,i.e. to a maximum particle size of around /8 to inch, followed by a rodmill or primary ball which in turn is followed by a secondary ball orpebble mill close circnited with a classifier which is in turn followedby one or more additional stages of grinding.

Several proposals have been made from time to time in the art in respectto reducing or eliminating the necessity for multiple stages in the wetreduction operation. One such proposal is described in Hadsell UnitedStates Patent No. 2,094,842 of October 5, 1937, where the material inthe form of a wet slurry as a run-of-mine or primary crusher product waselevated and dropped within a large diameter mill by means of buckets.Other proposals sought to overcome the difficulty through the use ofspecial mill cross-sectional shapes designed to accommodate both largeand small particles of feed in the pulp within the mill on the theorythat the larger lumps of material could be made, in the course of theirown reduction, to act "as reduction media upon the smaller particles.

Although certain of these prior proposals have had limited success,especially as regards smaller milling units designed to producerelatively low tonnages, there has not as yet been a proposal for wetreduction which has effectively solved the existing problems on acommercial scale of operation.

I have now found that the above enumerated dithculties may be largelyovercome and an effective Wet milling of run-of-mine or coarse crushedmaterials can be carried out by employing as a milling unit a noveldesign of mill adapted to perform a wet milling operation on the basisof principles previously applied by me to the reduction of materials inthe dry state.

A wet reduction mill according to the present inven tion broadlycomprises a cylindrical drum having a diameter which is at least twicethe length thereof and which is mounted for rotation about asubstantially horizontal axis. Said drum is provided about its interiorperiphery with a plurality of highly upstanding transverse crusher barsspaced apart a suflicient distance fully to. accommodate and engage thelargest particles of the material which is to be used as feed to themill. Additionally, there are mounted on the end walls of the said drumannular liners which extend inwardly into the interior of the drum asubstantial distance, as will hereinafter be defined in greater detail,so as to present a frusto-conical surface facing the peripheral regionsof the mill and concentric the axis thereof, which frusto-conicalsurface is so positioned as to maintain during operation of said mill 2keying action zone in the space between said annular liners and theperiphery.

In my prior United States Patent No. 2,704,636, I disclosed thesignificance of the maintenance of a keying action zone in connectionwith combined dry crushing and grinding mills. In connection with suchdry mills,

2 the principal eifect of the keying action resides in the maintenanceof the charge the keying zone as a more compact mass which more readilyabsorbs useful grinding Work input so that for a milling unit of givensize working on a given ore the capacity of the unit is increasedsubstantially.

I have found surprisingly that in connection with wet milling themaintenance of a keying action zone produces the further advantage thatit permits the element of pulp density to be to a substantial extentdisregarded insofar as its elfect upon circulation of the charge isconcerned. Thus, the keying of the charge enables the use of high pulpdensities enabling a greater amount of solid material to be usefullyworked upon in the charge, and hence making possible such increases incapacity as render practical the application of large diameter shortlength mills to the wet reduction of materials which hitherto haverequired plurality of stages of wet reduction in conventional equipmentwith the attendant advantages of saving of plant space, capital cost andother advantages which flow from the ability to conduct a reductionoperation as a unit process rather than as a series of separate stageswhich require detailed integration and expansive plant layout.

A number of different embodiments are contemplated by'the presentinvention having regard to the nature of the operation intended and thecharacteristics of the material which is to be treated.

In connection with operations requiring a product of fine particle size,e.g. of the order of size which might normally be produced inconventional plant operations where one or more secondary ball mills areemployed, the mill of the present invention is so designed as to providefor discharge through grates in the downstream mill trunnion.

Where the mill product is intended to be of a coarser particle size ingeneral it is preferred so to construct the as to provide for peripheraldischarge through grates situated at the periphery. With peripheralgrate discharge, the mill may be provided with a false wall and liftersso as to conduct the peripherahy discharged material radially inwardlyfor flow out through the downstream trunnion. According to a furtherembodiment of the invention and in particular where it is desired tooperate at high pulp densities and especially where the material beingreduced is of a very fine grain structure and is readily broken down,the peripheral grate may be exposed, and means provided for scraping orsluicing the mill discharge product for conduction by suitable means toa classifier or screen. Where, as in the case just discussed, theviscosity cf the product is so high that effective flowability of themill discharge cannot be obtained without the use of scrapers, sluicersand the like, there are various means which may be applied to deliverthe dis charge from the In some instances, use may be made of anairstream, high velocity air jets, steam jets and the like. Similarly,in connection with trunnion overflow discharge, in addition to steam,air and water jets, various mechanical arrangements are known in the artwhich may be used to assist transfer, such as screws, lifters, buckets,scrapers and the like. In this specification and in the appended claims,when I use the expression assisted discharge, I contemplate, unlessotherwise specified, that any of such means may be employed whether inreference to peripheral or to trunnion overflow discharge.

The invention and its operation will be more completely understood fromthe following detailedspecification in conjunction with the accompanyingdrawings wherein:

FIGURE 1 is a vertical cross section through the axis of a millaccording to one embodiment of the invention 3 provided with trunnionoverflow grate discharge means;

FIGURE 2 is an end view of the mill illustrated in FIGURE 1 taken fromthe discharge side thereof and illustrating details of the gratedischarge; v

FIGURE 3 is a perspective of the general layout of a mill according tothe present invention illustrated in closed circuit with a spiralclassifier;

FIGURE 4 is a top elevation of the layout illustrated in FIGURE 3;

FIGURE 5 is a fragmentary perspective view illustrating peripheraldischarge with lifters for returning mill product for discharge throughthe downstream trunnion thereof; V

FIGURE 6 is a fragmentary perspective view of a preferred form oftrunnion grate discharge;

FIGURE 7 is a fragmentary perspective view of a mill according to theinvention illustrating peripheral grate discharge directly from theperiphery of the mill;

FIGURE 8 is a fragmentary detail section illustrating the flow path ofthe mill product illustrated in the embodiment of FIGURE 7;

FIGURES 9, 10 and D1 are fragmentary cross-sectional detailsillustrating various alternative forms of structure for the annularliners which establish a keying action zone within the mill.

Referring now more particularly 'to the drawings wherein like numeralsrefer to like parts throughout, the mill illustrated in FIGURES 1 and 2has the end walls 11 and 12 separated by the peripheral cylindrical wall13. As is apparent from the drawing, the length of the peripher'alcylindrical wall 13 is short compared to the diameter of the end walls11 and 12, the peripheral internal diameter length ratio being at least2:1. The radial ribs 14 are provided to strengthen the end walls 11 and12 structurally and trunnion flanges 16 and 17 extend outwardly from theend walls 11 and 12 concentrio with the axis thereof to provide thejournal bearing surfaces 18 and 19 on which the mill is supported forrotation.

Spaced about the interior of the peripheral cylindrical wall 13 are thehighly upstanding crusher bars 20 which are held in place by appropriatebase and retaining plates in a manner such for instance as that which isillustrated in my prior United States Patent No. 2,555,171 where asimilar type of crusher bar construction is illustrated.

' On the interior of each end wall 11 and 12, there are mounted the ringshaped liner elements 21 and 22 and the annular keying liner elements 23and 24. As illustrated, the latter keying liner elements each have twocircular radially spaced apart apices 25 and 26 presenting keyingsurfaces 27 and 28 respectively in the direction of the periphery of themill. Other forms of keying liner elements may replace keying linerelements 23 and 24 depending upon the nature of the operation and typeof ore to be treated. Three such alternative forms are illustrated inFIGURES 9, 10 and 11 which are generally preferred for particularpurposes which will be hereinafter described.

The trunnion flange 17 is formed to provide a conical interior surface29 having an interior flanged lip 30 over which projects the lip 31 ofthe feed chute 32 whereby to provide a flow path into the mill for feedmaterial and make-up water and oversize return which are delivered bydelivery chute 33.

Mounted in the trunnion flange 16 is a grate discharge 34 which isformed with the generally conical inner surface 35 and the grateindicated generally at 36. The grate is formed with a solid interiorportion 37 surrounded by the radially open grate structure 38, the wholebeing supported rigidly the portion 35 by the bracer elements 39 whichalso function as lifters in assistingthe discharge of material throughthe grates.

Mounted at the periphery of the end wall 12 in the drive girth gear 40,which is driven throughpinion 41 (see'FIGURE 3), which in turn is drivenby the electric motor '42 through speed reducer 43. I

The mill discharge is deposited in a classifier feed box 44 and is fedinto the spiral classifier 45, the product being discharged at theclassifier overflow at 46, the oversize being returned together with themake-up water provided by supply 47 tothe delivery chute 33, whichdelivers it to the feed chute 32 where it returns to the mill to getherwith the mill feed which is delivered to the feed chute by conveyor 47a.

Alternatively, the discharge from the mill may pass directly to ascreen, the undersize going directly tometallurgy and the oversize beingrecirculated to the mill, e.g. by conveyor. I

' The flow paths of discharge fi'om the mill are indicated generallywith relation to theembodiment illustrated in FIGURES 1 and 2 in thefragmentary perspective shown in FIGURE 6.

A form of peripheral grate discharge is shown in FIG- URE 5. In thisembodiment, the mill is provided with the false inner wall 50 having theradially disposed peripheral grate openings 51 adjacent the cylindricalperipheral wall of the mill. The end wall -11 of the mill is separatedfrom the false inner wall 50 by a plurality of radially disposed lifters52 which carry mill discharge radially inwards where it is deflected bythe conical surface 53 of the central portion of the false wall 50 whichoverlies the trunnion opening and is permitted to flow over the trunnionliner member 54 for discharge, the flow paths being substantially asillustrated.

In this embodiment, it is to be understood that the peripheralcylindrical wall 13 forms a water-tight closure with the end wall 11 sothat the grate 51 and lifters 52 are completely closed at the periphery.

An alternative form of peripheral grate discharge is illustrated inFIGURE 7. In this instance, the false inner wall 50 of the mill, theradially disposed peripheral grates 51 and lifters 52 are disposed inthe same manner as in FIGURE 5, but in this case, the inner extremity ofthe space between the false wall 50 and the wall 11 is sealed oil by theflange 53A whereas the peripheral cylindrical wall 13 is provided with aplurality of discharge grates 54 permitting the mill discharge to passdirectly radially outwardly for collection in the trough 55, the flowpaths being illustrated in FIGURE 7 and in substantially greater detailin the section shown in detail in FIGURE 8.

The alternative forms of keying liners 23a, 24a, 23b, 24b, 23c and 240illustrated respectively in FIGURES 9, l0 and 11 may, as previouslymentioned, be substituted .for the forms of keying'liner 23 and 24illustrated in FIGURE 1. The particular function of these liner elementswill be described in connection with the operation of the inventionwhich follows.

In relation to operation of the invention, it is necessary first of allto take into account the type of feed which is to be fed to the mill. Inthis connection, it is important to note that the spacing of the crusherbars must be such as to prevent wedging of individual pieces of largefeed so that the space between the crusher bars is such as to providefor effective engagement by the crusher bars 13 of the largest particlesof feed.

Secondly, account must be taken of the reduction characteristics of thematerial. If the material is tough, the breakdown of the largest pieceswill be more gradual than the breakdown of such large pieces will be ifthe material breaks down readily, and consequently where the material istough, the most effective keying action will be achieved if a relativelylarge keying zone is provided. If the large pieces of material breakdown quite readily, it will be necessary to reduce the size of thekeying zone in order to maintain efiective keying action. Some materialsbreak down readily at the largest particle size, but tend to formsomewhat tougher pebbles at an intermediate size range, and with suchmaterials it'may be desired to establish zones within 1 the keying zoneespecially adapted to develop the maximum keying effect from the mixturein the charge consisting of relatively few of the largest pieces and arelatively large'number of such pebbles. Y Y

Thirdly, the ultimate particle size er the product to be produced mustbe taken into account, and once again, having regard to the factorsalreadydiscussed, aselec tion must be made between trunnion dischargeand overflow discharge. Generally speaking trunnion overflow gratedischarge is, preferred for fine grinding applications especiallywherethe flowability of the pump is reasonable, within the range er pulpLdensities which must be used having regard tothe follow-up plant. Forcoarse grinding applications, peripheral grate discharge with flowdirected back to- ,the ;trunnior 'i as illustrated in FIGURE 5.ispreferred. However, where the ilowability of the pulp discharged fromthe -ini1l is poor withinthe permissible range of pulp densities,peripheral grate discharge of the type illustrated in FIGURE 7 will beused. It will be' appreciated that in any of, the foregoing cases usemay be made of assisted discharge of any suitable form in-order. toextend, the range of pulp densities in which the particular embodimentof the invention may be effectively used. 4

V The keying zone may be defined as. the space within 6 ofthe'surfa'cesf90 or 100 toprovide the optimum rela-' tive size of thekeying zone". The dotted lines 9011 and 90b illustrate how the design ofliners 23a and 24a may be modified to produce a larger relative keyingzone.

What I claim as my invention is: 'j

. 1. A wet combined crushing and grinding mill comprising;a'horizontally rotatable drum having a cylindrical wall and two endwalls, the ratio of the interior diameter of the drum to the interiorperipheral length thereof being at least 2: 1; a plurality of highlyupstanding transverse crusher bars mounted in spaced apart relationaround the cylindrical wall to eifectively engage the largest particlesof feed; meansfor feeding feed material,

- including liquid to said mill;'means for withdrawing the'mill lyingbetween the most radially inward'apic'es forming about 45 of the millvolume is preferred. The

effective zone sizes fortougher materials will be somewhat larger,while'those form'ore fiiable materials Will be somewhat smaller. v

The distance of lateral penetration of the api'ces of the keying linersinto the interior of the mill is also most important. This may bemeasured conveniently as the percentage of the length of the milesmeasured along a line through the apices of the keying liners which issubtended by the keying liners. The length of the mill thus measured istermed herein the efiective mill length. A relative penetrationof fromabout 20% to about 80% of the cifective mill volume represents theefiective range. Generally speaking, the more friablethe material thegreater penetration is desirable. For materials of medium grindablity apenetration of about 40% of the effective mill length is preferred whenoperating with a mill charge having good flow characteristics.

Where the material develops pebbles in the medium size ranges to alarger extent than normal, it may be desirable to have a number ofapices on each keying liner at varying distances from the periphery andwith varying penetrations, taking into consideration the relativevolumes of the various sized particles which are present in the millduring operation along the lines illustrated in FIGURE 11.

For fine grinding with trunnion overflow discharge an arrangement suchas is illustrated in FIGURE 1 is preferred. The surfaces 27 are designedto effectively key the larger pieces of material in the charge, whilethe surfaces 28 key the much larger mass of finer particles present, andin doing so permit the water and fine products to pass more rapidlytowards the mill axis. This results in a concentration of fines andwater at the trunnion overflow giving good flowability and a relativelylow viscosity despite the high pulp density of the charge taken as awhole. This is an outstanding advantage of the present invention.

The arrangements illustrated in FIGURE 9 or 10 are more suitable, in thecase of peripheral discharge. Here there is no desire to concentrate thefines and water at the mill axis and the governing factor is thelocation product comprising solids and liquids from said mill; and apair of opposed annular keying liners mounted one on each of the endwalls of the drum, said keying liners collectively penetrating. into themill interior from about 20% to about of the elfective length, anddefining a keying zone which is from about 30% to about 75% of theefiective mill volume.

2. A Wet combined crashing and grinding mill comprising; a horizontallyrotatable drum having a cylindrical wall and two end walls, the ratio ofthe interior diameter of the drum to the interior peripheral lengththereof being at least 2:1; a plurality of highly upstanding transversecrusher bars mounted in spaced apart relation around the cylindricalwall to effectively engage the largest particles of feed; means forfeeding feed material, including liquid to said mill; grate means forwithdrawing product comprising solids and liquids from said mill; and apair of opposed annular keying liners mounted one on each of the endwalls of the. drum, said keying liners collectively penetrating into themill interior from about 20% to about 80% of the efiective mill length,and defining a keying zone which is from about 30% to about 75% of theeffective mill volume.

'3. A wet combined crushing and grinding mill comprising; a horizontallyrotatable drum having acylindrical wall and two end walls, the ratio ofthe interior diameter of the drum to the interior peripheral lengththereof being at least 2:1 a plurality of highly upstandingtransversecrusher bars mounted in spaced apart relation around the cylindricalwall to effectively engag'ethe larg est particles of feed; means forfeeding feed material, including liquid to said mill; peripheral. gratemeans for withdrawing product comprising solids and liquids from saidmill; and a pair of opposed annular keying liners mounted one on each ofthe end walls of the drum, said keying liners collectively penetratinginto the mill interior from about 20% to about 80% of the efiective milllength, and defining a keying zone which is from about 30% to about 75%of the effective mill volume.

4. A wet combined crushing and grinding mill comprising; a horizontallyrotatable drum having a cylindrical wall and two end walls, the ratio ofthe interior diameter of the drum to the interior peripheral lengththereof being at least 2:1; a plurality of highly upstanding transversecrusher bars mounted in spaced apart relation around the cylindricalwall to effectively engage the largest particles of feed; means forfeeding feed material, including liquid to said mill; trunnion overflowgrate means for withdrawing product comprising solids and liquids fromsaid mill; and a pair of opposed annular keying liners mounted one oneach of the end walls of the drum, said keying liners collectivelypenetrating into the mill interior from about 20% to about 80% of theeffective mill length, and defining a keying zone which is from about30% to about 75 of the efiective mill volume.

5. A mill as defined in claim 2, in which said keying linerscollectively penetrate into the mill interior about 40% of the effectivemill length, and define a keying zone which is about 45% of theeffective mill volume.

6. A mill as defined in claim 4 which comprises a false end wall in saiddrum mounted so as to leave a space between the same and the end wall ofthe mill, a plurality 7 of radial grate openingstabout the periphery ofsaid false wall; a pluralityof radial. lifters between said false wall,

and end wall, and fiow'directingmeans for directing mill product fromsa'id lifters outwardly through the mill trunnion. e 7. A-mill asdefined in claim 4 comprising a false wall s'paced' apart'from' the endwall of the mill; a plurality of radial grate openings about theperiphery of said false wall; a plurality of openings in the cylindricalwall of the mill arranged to permit peripheral'discharge of mill productwhich is passed through said grate openings, and means forcollecting thedischarge from said openings. 8. A mill as defined in claim .6,;whereinmeans are provided for accomplishing assisted discharge of mill product.7 V p p i 9. A mill as defined in claim7, wherein means are provided foraccomplishing assisted discharge of mill product. 7

10. A method for the wet comminution of rock, ores and the like whichcomprises feeding solid and liquid feed material to a materialreducti'onmill having a cylindrical wall and two end walls, the ratio ofthe interior diameter of the drums to the interior peripheral lengththereof being at least 2:1, a plurality of highly upstanding transversecrusher bars mounted in spaced apart re- 8 2 0% to about 80% of theefiiective mill length, said keying zone being from about 30% to about75% ofthe effective mill volume, withdrawing the product from said millbygrate means, and collecting said product.

12. A method for thewet comminution or rock, ores and the likewhich-comprises feeding solid and "liquid feed material toa materialreduction mill having a cylindrical wall and two end walls, the ratio orthe interior diameter of the drum to the interior peripheral lengththereof being at least 2:1, a plurality of highly 'upstand ingtransverse crusher bars mounted in spaced apart relation around thecylindrical wall efiectively engage the largest particles of feed,maintaining during operation akeynig action zone defined by thepariphery 0f themill and a pair of opposed annular keying liners mountedone on each of the'end walls of the drum,' said keying-linerscollectively'penetrating into the mill interior from about 7 mill byperipheral. grate means, and collecting said lation around thecylindrical wall to etfectively engage t the largest particles of feed,maintaining during operation a keying action Zone defined by theperiphery of the mill and a pair of opposed annular keying linersmounted on each of the end walls of the drum, said keying linerscollectively penetrating into the mill interior from about 20% to about80% of the effective mill length, said keying zone being from about 30%to 75% of the effective mill volume; withdrawing and collecting theproduct of said mill.

11'. A method for the wet comminution of rock, ores and the like whichcomprises feeding solid and liquid feed material to a material reductionmill having a cylindrical wall and two end walls, the ratio of theinterior diameter of the. drums to the interior peripheral lengththereof being at' least 2:1, the plurality of highly upstandingtransverse crusher bars mounted in spaced relation around thecylindrical wall to eifectively engage the largest particles of feed,maintaining during operation a keying action zone defined by theperipheryiof the mill and Ya pair of opposed annular keying linersmounted oneon each of the end walls of the drum, said keying linerscollectively penetrating into the. mill interior from about product. I

, 13. A method for thewet comminution of rock, ores and the like whichcomprises feeding solid and liquid feed material to a material reductionmill'having a cylindrical wall and two end walls, the ratio of theinterior diameter of the drum to the interior peripheral length thereofbeing at least 2:1, a plurality of highly upstanding transyerse crusherbars mounted in spaced apart relation around the cylindrical wall to,eflectively'engage the largest particles of feed; maintaining duringoperation a keying action zone defined by the periphery of the mill anda pair of opposed annular keying liners mounted one on each of the-endwalls of the, drum, said keying liners collectively penetrating into themill interior from about 20% to about 80% of the effective mill length,said keying zone I Williamson' Apr. 25-, 1922 1,670,005 7 Pratt May 15,1928 2,704,636 Weston Mar. 22, 1955 Klugh. July 10, 1956

